1. Field of the Invention
This invention relates to an evaporative fuel-processing system for internal combustion engines, which prevents emission of evaporative fuel generated in a fuel tank of the engine, into the atmosphere during refueling.
2. Prior Art
FIG. 1 shows a conventional evaporative fuel-processing system for internal combustion engines, which is known from U.S. Pat. No. 4,714,172. In the figure, a fuel tank 101 communicates through a filler tube (fuel supply pipe) 102, a diaphragm valve 107 and a passage 112 with a canister 114 accommodating an adsorbent therein. The diaphragm valve 107 has a first chamber 107a and a second chamber 107b defined by a diaphragm 108. The first chamber 107a communicates through a passage 106 with an upper end of the filler tube 102, while the second chamber 107b always communicates with a passage 111 and can communicate with the passage 112 when the valve is opened. A valve element 109 is mounted on the diaphragm 108, for closing and opening the passage 112. A spring 110 is arranged in the first chamber 107a, for biasing the diaphragm 108 in a direction of closing the valve.
Mounted in the filler tube 102 at a location between open ends of the passages 106 and 111 opening into the tube 102 is a shutter valve 103 having a valve element formed with a small hole, not shown. The fuel tank 101 and the canister 114 are connected to an intake passage of the engine, not shown.
With the above arrangement, when the upper end of the filler tube 102 is closed by a fuel cap 104, pressure within the first chamber 107a and pressure within the second chamber 107b are equal to each other, whereby the diaphragm valve 107 is kept in a closed position. On the other hand, when the cap 104 is removed at refueling, the pressure within the first chamber 107a lowers to the atmospheric pressure, and hence the diaphragm 108 and the valve element 109 of the diaphragm valve 107 are displaced leftward as viewed in the figure, to open the valve 107, whereby evaporative fuel generated in the fuel tank 101 is introduced into the canister 114.
According to the above conventional system, however, if the fuel cap 104 is inadvertently not tightened after completion of refueling, the following inconvenience arises: That is, when the temperature of fuel elevates so that evaporative fuel is generated in large amounts, evaporative fuel is unfavorably discharged through the small hole, not shown, of the shutter valve 103 to the atmosphere.